Patterns of Tannin Accumulation in Leaves of C-4 Euphorbia maculata

C-4 Euphorbia maculata 엽육조직 내 탄닌물질의 축적 양상

  • 김인선 (계명대학교 자연과학대학 생물학과)
  • Published : 2003.09.01

Abstract

Patterns of tannin accumulation in leaves of C-4 Euphorbia maculata have been examined using electron microscopy. Tannins, which are secondary metabolite phenolic compounds, were found to be deposited conspicuously in vacuoles of certain tissues regardless of their stage in development. However, patterns of deposit accumulation were distinguishable by their cell type during leaf differentiation. The deposits appeared most concentrated in the concentric bundle sheath cells enclosing veins, while little or no density was detected mostly in the mesophyll cells close to the epidermis. An ultrastructural study revealed that the deposits were restricted to the vacuoles at an early stage of leaf development; during which the vacuoles were almost completely filled with the tanniferous substances. The deposits themselves took different forms ranging from granules to huge globules while expanding leaf blade. As the leaf matured, the deposits accumulated either centripetally adjacent to the inner tangential tonoplast or by penetration into the cytoplasm amongst various cellular organelles, resulting in an extremely dense cytoplasm. Electron micrographs frequently showed the delineation of each organelle by the presence of dense deposits within the cytoplasm. Some large depository vacuoles filled with tannins had a corrugated appearance on the sectioned surface. The pattern and potential role of the deposits have been discussed.

유액을 형성하는 대극과 C-4 식물 Euphorbia maculata의 엽육조직은 유관속초와 엽육세포 두 유형의 유세포로 분화되는데, 본 연구에서는 이들 세포 내에 축적되는 2차 대사물질인 탄닌의 발달양상을 형태 구조적으로 연구하였다. 탄닌의 축적은 엽육조직 발달초기 상태에서부터 시작되어 유관속초세포에서 뚜렷하게 진행되었고, 분화를 마친 성숙한 잎의 유관속초세포와 인접한 엽육세포에는 현저하게 다른 양상으로 축적되었다. 일부 미분화 유관속초세포는 발달초기에 일어난 액포융합현상으로 세포용적의 대부분을 차지하는 거대한 탄닌액포를 형성하여 세포질에는 영향을 미치지 않으나, 이후 엽육조직이 발달하면 유관속초세포 내 액포에는 소과립상에서부터 소구체, 구체 및 비교적 커다란 탄닌액포에 이르기까지 다양한 형태로 집적되었다. 특히, 탄닌이 세포소기관들 사이로 침투하여 소기관들의 경계를 따라 분포되거나, 침착이 더욱 진행되어 세포질 내 거의 모든 세포소기관에 영향을 미친 경우에는 세포질의 전자밀도를 매우 높게 나타났다. 반면, 엽육세포층 내에서는 탄닌의 축적현상이 드물게 일어나 대부분의 세포들은 거의 영향을 받지 않는 것으로 나타났다. 그러나, 유관속초세포 내 탄닌의 축적현상이 할발하게 일어난 경우에는 이들과 바로 인접한 엽육세포의 세포질에도 탄닌의 축적이 야기되어 일부 세포소기관의 전자밀도는 높게 나타났다. Euphorbia maculata는 식물체 전체에 망상으로 분포하는 유관에 다량의 알카로이드성 유액이 분비되는데, 액포 및 세포질에 축적되는 이러한 탄닌은 이들 알카로이드성 물질과 밀접한 관계를 유지하며 병충해 및 초식동물로부터의 보호 등 식물체 방어기작에 중요한 기능을 수행할 것으로 추정된다.

Keywords

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